Refrigeration unit with defrost heater



Aug 3, 1954 s. BARTLOWE REFRIGERATION UNIT WITH DEF'ROST HEATER Filed April 29, 1952 [Nl/ENTO/Q.

Patented Aug. 3, 1954 REFRIGERATION UNIT WITH DEFROST HEATER Sterling Bartlowe, Adrian, Mich., assignor to Bohn Aluminum & Brass Corporation, Detroit, Mich.

Application April 29, 1952, Serial No. 285,014

(Cl. 21S-19) 4 Claims. l

The present invention relates to a refrigeration unit provided with a defrost heater, as well as to a method for producing the new refrigeration unit.

The invention provides a defrost heater that is formed in situ on the refrigeration unit. The defrost heater can be produced very inexpensively but is highly efficient in operation, since it makes efiicient use of the electrical current supplied to the heater.

Most of the systems now in use for defrosting refrigeration units involve the use of separate rod heaters filled with magnesium oxide filler. These heaters are relatively expensive and because of their fixed shape they can be applied to a refrigeration unit only in certain limited places.

It has also been proposed to apply a separatelyformed heating blanket to certain flat surfaces of a refrigeration unit, as in Cowgill Patent No. 2,515,294. This system also is expensive and of limited application.

According to the present invention the defrost heater is formed directly on the surface of the refrigeration unit. This is done by applying to the surface of the refrigeration unit first a layer of insulating material, then a layer of material which will form an electrical resistance element, and the heater is finally covered with another layer of insulating and protecting material. These layers may be applied by spraying, brushing, etc.

Since the defrost heater is built up directly on the surface of the refrigeration unit, it can follow any irregular contour of the refrigeration unit. For example, it can follow a tube projecting from the surface of the refrigeration unit, or it can follow a depression in the surface. Since refrigeration units are often formed with irregular surfaces this ability to follow irregularities without added cost or complication is a very important feature of the present invention. These and other objects of the invention will become apparent as the description proceeds.

In the drawings:

Fig. 1 is a perspective View of a domestic evaporator embodying the invention.

Fig. 2 is a fragmentary cross section through one of the refrigeration tubes of Fig. 1.

Fig. 3 is a fragmentary cross section through one of the terminals of the defrost heater.

Fig. 4 is a cross section through a tubular evaporator unit provided with the defrost heater.

Fig. 5 is a View similar to Fig. 1 but showing an alternate arrangement of the defrost heater Vith relation to the surface of the evaporator.

Referring to Fig. l more specifically, a tube I0 for carrying refrigerant is attached to, or forms part of, the body II of the evaporator. Ends I2 and I3 of the tube project for connection to the refrigeration system. An accumulator I4 is inserted in the refrigerant tubing. These parts are of well-known construction and may be formed of aluminum or other suitable material.

The defrost heater which is indicated generally at I5 in Fig. l is shown in greater detail in Fig. 2. This heater element is built up in situ in the following manner:

A first layer of electrical insulating material i5 is deposited on the surface of the refrigerating unit. This electrical insulating material may be formed of organic or inorganic material and it may be applied to the evaporator surface in the desired pattern by either spraying, dusting, brushing, dipping, or any other preferred method. lf the insulating material is applied in a liquid vehicle it is, of course, necessary to permit this vehicle to evaporate so as to deposit a firm layer of insulating material before the subsequent operations can be performed.

The reference numeral I'I refers to a layer forming an electrical heating element. This heating element layer I1 is built up by depositing a suitable electrical resistant material suspended in a Vehicle. For example, a phenolic resin or silicon resin paint, thinned with a suitable thinner and containing chrome nickel powder may be deposited on top of layer I6 by painting, spraying, or other suitable method. The layer Il' will, of course, be of less extent than layer I6 so that the edges of layer Il may be suitably protected and insulated.

The heater is completed by depositing a second layer I8 of material which will insulate and protect the heating element. The layer I8 completely covers and surrounds layer II in order to furnish complete electrical insulation. Layer I8 may be deposited in a manner described above in connection with layer I6.

The layers I6, I1 and I8 may be deposited with an air-drying vehicle, or with one which requires baking.

To provide for convenient attachment of electric Wires to conduct current to the heater I5 a connector I9 is attached to one end of heater I5 and a connector 20 is attached to the other end of the heater. The connectors I9 and 20 may have any suitable form, for example that illustrated in Fig. 3 in which an insulating bushing 2I fits through an opening formed in evaporator body H, the insulating coating l5, the heater element Il, and the protective coat I3. A terminal 22 formed of copper or other similar material which is a good conductor of electricity, is suitably imbedded in or connected to the heater element il' and is held in place by an insulating washer 23 secured by a nut 24.

In the form of the invention illustrated in Fig. 1 the heater I5 covers the upwardly projecting portion of refrigerant carrying tube Hi and extends down over a portion of the evaporator wall on each side of tube lil. rIhe heater i5 follows the pattern of tube It over substantially the entire length of the tube. .As a result of this construction the heat supplied by the heater to tube I is conducted directly to the refrigerant passing through tube l0, thereby raising the temperature of the refrigerant and using the refrigerant to help distribute the heat to the evaporator. In some cases it may not be necessary to use the heater over the entire length of tube Ill. The length of the heater i will depend upon a balance of factors. The longer the heater I5 the shorter time required for defrosting, while the shorter the heater l5 the less expensive the installation.

In some cases it may not be desirable to have the heater I5 blanket the tube I5, in which case an installation as illustrated in Fig. 5 may be used. In Fig. 5 the heater i5 is disposed between the runs of the tube l and at certain points, such as at 25 and 26, the heater may cross over tube l0. This construction is used where it is desired to apply less heat to the refrigerant and to apply more heat directly to the metal surface of the evaporator.

Fig. 4 illustrates the application of the invention to a tubular evaporator member 2l. I-Iere the heater i5, which is built up of three separate layers as previously described, completely surrounds the evaporator tube` Suitable terminals analogous to those described above are used to conduct electricity to the heater element.

It should be understood that in Figs. 1 and 5 the electrical heater element is illustrated in a partially diagrammatic manner. For more accurate details reference should be made to Figs. 2 and 3.

The phrase irregular surface used in the appended claims is meant to cover any surface which is other than planar, such as a cylindrical body, or a planar surface having parts projecting from or depressed below the plane surface.

It will be clear to those skilled in the art that the present invention provides a simple and efficient defrost heater for a refrigeration unit. Because the heating element is associated very closely with the surface of the evaporator and extends over a considerable portion of the evaporator surface the heat from the heating element is used very efficiently by conduction, with the result that the refrigeration unit may be defrosted with less electrical current and in less time than with systems previously proposed.

According to the provisions of the patent statute, I have explained the principles of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practised otherwise than as specically illustrated and described.'

I claim:

1. In combination with a refrigeration unit of the type having a conduit projecting above a at surface, an electrical heater formed in situ on said surface, the heating element comprising: a rst layer of electrical insulating material bonded to the surface of the refrigeration unit and extending longitudinally over a considerable length of the conduit, and extending over the flat surface adjacent both sides of the conduit, but leaving other portions of the flat surface uncovered, a layer of electrically conductive material bonded to the nrst layer of electrical insulating material and of less extent than the rst layer of insulating material, a second layer of electrical insulating material covering and bonded to the electrical heating layer, the layer of electrically conductive material having two electrical terminals attached thereto at points separated from each other, and being otherwise covered on all sides by the insulating material, and serving as an electrical heating element to defrost the refrigeration unit.

2. In combination with a refrigeration unit of the type having a surface with a conduit projecting above the surface, said conduit being disposed sinuously relative to said surface, an electrical heater formed in situ on said surface, the heating element comprisingi a first layer of electrical insulating material bonded to the surface of the refrigeration unit and covering a major portion of the sinuous conduit and extending over the surface adjacent both sides of the conduit, but leaving other major portions of the surface uncovered, a layer of electrically conductive material bonded to the first layer of electrical insulating material and of less extent than the first layer of insulating material, a second layer of electrical insulating material covering and bonded to the electrical heating layer, the layer of electrically conductive material having two electrical terminals attached thereto at points separated from each other, and being otherwise covered on all sides by the insulating material, and serving as an electrical heating element to defrost the refrigeration unit.

3. In combination with a refrigeration unit of the type having a surface with a conduit projecting above the surface, said conduit being disposed sinuously relative to said surface, an electrical heater formed in situ on said surface, the heating element comprising: a first layer of electrical insulating material bonded to the surface of the refrigeration unit, and being disposed primarily between runs of the conduit, but crossing over the conduit at certain points, a layer of electrically conductive material bonded to the rst layer of electrical insulating material and of less extent than the first layer of insulating material, a second layer of electrical insulating material covering and bonded to the electrical heating layer, the layer of electrically conductive material having two electrical terminals attached thereto at points seaprated from each other, and being otherwise covered on all sides by the insulating material, and serving as an electrical heating element to defrost the refrigeration unit.

4. In combination with a refrigeration unit of the type having a conduit projecting abcve a flat surface, an electrical heater formed in situ on said unit, the heating element comprising: a rst layer of electrical insulating material bonded to the surface of the refrigeration unit and extending in a pattern covering part of said conduit and part of the flat surface, but leaving majcr portions of the flat surface uncovered, a layer of electrically conductive material bonded to the 5 6 first layer of electrical insulating material and Number Name Date of less extent than the rst layer of insulating 1,742,062 Day Dec. 31, 1929 material, a second layer of electrical insulating 1,767,715 Stoekle June 24, 1930 material covering and bonded to the electrical 2,008,628 Ruil July 16, 1935 heating layer, the layer of electrically conductive 5 2,205,543 Rideau et al. June 25, 1940 material having two electrical terminals attached 2,276,454 Becker Mar. 17, 1942 thereto at points separated from each other, and 2,410,194 Baker Oct. 29, 1946 being otherwise covered on all sides by the in- 2,515,294 Cowgill July 18, 1950 sulating material, and serving as an electrical HER heating element to defrost the refrigeration unit. 10 OT REFER'ENCES New Advances in Printed Circuits, National References Cited in the le of this patent Bureau of Standards Miscellaneous Publication UNITED STATES PATENTS 192, page 15. Issued Nov. 22, 1948.

Number Name Date 905,045 Ayer et a1 Nov. 24, 190s 15 

